Polymorphisms in two key anthocyanic genes of clivia (Clivia miniata L.) reveal evidence of selection and possible association with flower pigmentation

Members of the genus Clivia show considerable variation in flower pigmentation and morphology. Such variation is affected by mutations that emerge in candidate flower development genes over time. Besides population history, mutations can further illuminate the effects of demographic events in populations in addition to population genetic parameters including selection, recombination, and linkage disequilibrium (LD). The current study aimed to find sequence variants in 2 anthocyanin biosynthetic genes (DFR and bHLH) of Clivia miniata and use the data to assess population genetic factors from a random collection of orange/red- and yellow-flowered specimens. Overall, average nucleotide diversity in the 2 anthocyanin genes was moderate (π = 0.00646), whereas haplotypes differed significantly (Hd ≥ 0.9). Gene evolution was seemingly driven by mutations (CmiDFR) or recombinations (CmibHLH001). LD decayed swiftly within the analyzed gene regions and supported the feasibility of assessing trait-variant associations via the association/linkage mapping approach. In the end, most associations were found to be spurious, but 1 haplotype in CmibHLH001 showed a promising correlation to the orange/red flower phenotype in Clivia specimens. In all, the present study is the first to measure gene-level diversity in C. miniata-data that had never been reported so far. Furthermore, the study also identified allelic and haplotypic variants that may be beneficial in future association genetic studies of Clivia. Such studies, however, consider large diverse populations to control for statistical bias intrinsic to the analysis of small datasets.

Reciprocal natural hybridization between Lycoris aurea and Lycoris radiata (Amaryllidaceae) identified by morphological, karyotypic and chloroplast genomic data

BACKGROUND

Hybridization is considered as an important model of speciation, but the evolutionary process of natural hybridization is still poorly characterized in Lycoris. To reveal the phylogenetic relationship of two new putative natural hybrids in Lycoris, morphological, karyotypic and chloroplast genomic data of four Lycoris species were analyzed in this study.

RESULTS

Two putative natural hybrids (2n = 18 = 4 m + 5t + 6st + 3 T) possessed obvious heterozygosity features of L. radiata (2n = 22 = 10t + 12st) and L. aurea (2n = 14 = 8 m + 6 T) in morphology (e.g. leaf shape and flower color), karyotype (e.g. chromosome numbers, CPD/DAPI bands, 45S rDNA-FISH signals etc.) and chloroplast genomes. Among four Lycoris species, the composition and structure features of chloroplast genomes between L. radiata and the putative natural hybrid 1 (L. hunanensis), while L. aurea and the hybrid 2, were completely the same or highly similar, respectively. However, the features of the cp genomes between L. radiata and the hybrid 2, while L. aurea and the hybrid 1, including IR-LSC/SSC boundaries, SSRs, SNPs, and SNVs etc., were significantly different, respectively. Combining the karyotypes and cp genomes analysis, we affirmed that the natural hybrid 1 originated from the natural hybridization of L. radiata (♀) × L. aurea (♂), while the natural hybrid 2 from the hybridization of L. radiata (♂) × L. aurea (♀).

CONCLUSION

The strong evidences for natural hybridization between L. radiata (2n = 22) and L. aurea (2n = 14) were found based on morphological, karyotypic and chloroplast genomic data. Their reciprocal hybridization gave rise to two new taxa (2n = 18) of Lycoris. This study revealed the origin of two new species of Lycoris and strongly supported the role of natural hybridization that facilitated lineage diversification in this genus.

Chimeric deletion mutation of rpoC2 underlies the leaf-patterning of Clivia miniata var. variegata

KEY MESSAGE

The deletion mutated rpoC2 leads to yellow stripes of Clivia miniata var. variegata by down regulating the transcription of 28 chloroplast genes and disturbing chloroplast biogenesis and thylakoid membrane development. Clivia miniata var. variegata (Cmvv) is a common mutant of Clivia miniata but its genetic basis is unclear. Here, we found that a 425 bp deletion mutation of chloroplast rpoC2 underlies the yellow stripes (YSs) of Cmvv. Both RNA polymerase PEP and NEP coexist in seed-plant chloroplasts and the β″ subunit of PEP is encoded by rpoC2. The rpoC2 mutation changed the discontinuous cleft domain required to form the PEP central cleft for DNA binding from 1103 to 59 aa. RNA-Seq revealed that 28 chloroplast genes (cpDEGs) were all down-regulated in YSs, of which, four involved in chloroplast protein translation and 21 of photosynthesis system (PS)I, PSII, cytochrome b6/f complex and ATP synthase are crucial for chloroplast biogenesis/development. The accuracy and reliability of RNA-Seq was verified by qRT-PCR. Moreover, the chlorophyll (Chl) a/b content, ratio of Chla/Chlb and photosynthetic rate (Pn) of YS decreased significantly. Meanwhile, chloroplasts of the YS mesophyll cells were smaller, irregular in shape, contain almost no thylakoid membrane, and even proplastid was found in YS. These findings indicate that the rpoC2 mutation down-regulated expression of the 28 cpDEGs, which disturb chloroplast biogenesis and its thylakoid membrane development. Thus, there are not enough PSI and II components to bind Chl, so that the corresponding areas of the leaf are yellow and show a low Pn. In this study, the molecular mechanism of three phenotypes of F1 (Cmvv ♀ × C. miniata ♂) was revealed, which lays a foundation for the breeding of variegated plants.

Phylogeny and adaptive evolution of subgenus Rhizirideum (Amaryllidaceae, Allium) based on plastid genomes

The subgenus Rhizirideum in the genus Allium consists of 38 species worldwide and forms five sections (A. sect. Rhizomatosa, A. sect. Tenuissima, A. sect. Rhizirideum, A. sect. Eduardia, and A. sect. Caespitosoprason), A. sect. Caespitosoprason being merged into A. sect. Rhizomatosa recently. Previous studies on this subgenus mainly focused on separate sections. To investigate the inter-section and inter-subgenera phylogenetic relationships and adaptive evolution of A. subg. Rhizirideum, we selected thirteen representative species, which cover five sections of this subgenus and can represent four typical phenotypes of it. We conducted the comparative plastome analysis with our thirteen plastomes. And phylogenetic inferences with CDSs and complete sequences of plastomes of our thirteen species and another fifty-four related species were also performed. As a result, the A. subg. Rhizirideum plastomes were relatively conservative in structure, IR/SC borders, codon usage, and repeat sequence. In phylogenetic results, the inter-subgenera relationships among A. subg. Rhizirideum and other genus Allium subgenera were generally similar to the previous reports. In contrast, the inter-section relationships within our subgenus A. subg. Rhizirideum were newly resolved in this study. A. sect. Rhizomatosa and A. sect. Tenuissima were sister branches, which were then clustered with A. sect. Rhizirideum and A. sect. Eduardia successively. However, Allium Polyrhizum Turcz. ex Regel, type species of A. sect. Caespitosoprason, was resolved as the basal taxon of A. subg. Rhizirideum. Allium siphonanthum J. M. Xu was also found in clade A. subg. Cyathophora instead of clade A. subg. Rhizirideum. The selective pressure analysis was also conducted, and most protein-coding genes were under purifying selection. At the same time, just one gene, ycf2, was found under positive selection, and another three genes (rbcL, ycf1a, ycf1b) presented relaxed selection, which were all involved in the photosynthesis. The low temperature, dry climate, and high altitude of the extreme habitats where A. subg. Rhizirideum species grow might impose intense natural selection forces on their plastome genes for photosynthesis. In summary, our research provides new insights into the phylogeny and adaptive evolution of A. subg. Rhizirideum. Moreover, we suggest that the positions of the A. subg. Rhizirideum species A. polyrhizum and A. siphonanthum should be reconsidered.

Cathepsin B-like cysteine protease ApCathB negatively regulates cryo-injury tolerance in transgenic Arabidopsis and Agapanthus praecox

Cell death is an inevitably cryo-injury in cell and tissue cryopreservation. The research on programmed cell death (PCD) in plant cryopreservation is still in its infancy. In this study, the survival rate of Agapanthus praecox embryogenic callus was significantly improved when the vitrification solution was added with 20 μM E-64, which is an inhibitor of cathepsin B. For further investigating the relation between cathepsin B and cryo-injury, the coding gene of cathepsin B, ApCathB was isolated and characterized. A subcellular localization assay showed that ApCathB was located in cytomembrane. Heterologous overexpression of ApCathB reduced the recovery rate during Arabidopsis seedlings cryopreservation from 29.56 % to 16.46 %. Transgenic seedlings lost most of cell viability in hypocotyl after dehydration and lead to aggravated cryo-injury. The reduced survival rate of ApCathB-overexpressing embryogenic callus of A. praecox further confirmed its negatively function in cryo-injury tolerance. In addition, the survival of ApCathB-overexpressing lines was almost rescued by E-64. TUNEL detection showed intensified signal and ROS was burst, especially for H₂O₂. Furthermore, VPE, Metacaspase 1, Cyp15a and AIF genes related to cell death regulation were remarkably up-regulated in ApCathB-overexpressing embryogenic callus during cryopreservation. Additionally, the expression level of genes regulating cell degradation was also elevated, indicating accelerated cell death caused by ApCathB-overexpressing. Taken together, this work verified that ApCathB negatively regulated the cryo-injury tolerance and cell viability through mediating the PCD event in plant cryopreservation. Significantly, cathepsin B has potential to be a target to improve survival rate after cryopreservation.

Complete chloroplast genomes shed light on phylogenetic relationships, divergence time, and biogeography of Allioideae (Amaryllidaceae)

Allioideae includes economically important bulb crops such as garlic, onion, leeks, and some ornamental plants in Amaryllidaceae. Here, we reported the complete chloroplast genome (cpDNA) sequences of 17 species of Allioideae, five of Amaryllidoideae, and one of Agapanthoideae. These cpDNA sequences represent 80 protein-coding, 30 tRNA, and four rRNA genes, and range from 151,808 to 159,998 bp in length. Loss and pseudogenization of multiple genes (i.e., rps2, infA, and rpl22) appear to have occurred multiple times during the evolution of Alloideae. Additionally, eight mutation hotspots, including rps15-ycf1, rps16-trnQ-UUG, petG-trnW-CCA, psbA upstream, rpl32-trnL-UAG, ycf1, rpl22, matK, and ndhF, were identified in the studied Allium species. Additionally, we present the first phylogenomic analysis among the four tribes of Allioideae based on 74 cpDNA coding regions of 21 species of Allioideae, five species of Amaryllidoideae, one species of Agapanthoideae, and five species representing selected members of Asparagales. Our molecular phylogenomic results strongly support the monophyly of Allioideae, which is sister to Amaryllioideae. Within Allioideae, Tulbaghieae was sister to Gilliesieae-Leucocoryneae whereas Allieae was sister to the clade of Tulbaghieae- Gilliesieae-Leucocoryneae. Molecular dating analyses revealed the crown age of Allioideae in the Eocene (40.1 mya) followed by differentiation of Allieae in the early Miocene (21.3 mya). The split of Gilliesieae from Leucocoryneae was estimated at 16.5 mya. Biogeographic reconstruction suggests an African origin for Allioideae and subsequent spread to Eurasia during the middle Eocene. Cool and arid conditions during the late Eocene led to isolation between African and Eurasian species. African Allioideae may have diverged to South American taxa in the late Oligocene. Rather than vicariance, long-distance dispersal is the most likely explanation for intercontinental distribution of African and South American Allioideae species.

Assessment of differences in morphological and physiological leaf lodging characteristics between two cultivars of Hippeastrum rutilum

BACKGROUND

Environmental lodging stress, which is a result of numerous factors, is characterized by uncertainty. However, several studies related to lodging in cereal crops have reported that lodging in the Hippeastrum rutilum environment is very rare. Hippeastrum rutilum is a garden flower with high ornamental value and abundant germplasm resources. Under past cultivation practices, it was found that the plant types of 'Red Lion', with red flowers, and 'Apple Blossom', with pink flowers, are quite different. The leaves of 'Red Lion' are upright, while the leaves of 'Apple Blossom' show lodging, which seriously affects its ornamental value. The aims of this study were to compare the differences between the two varieties with leaf lodging and upright leaves according to morphological and physiological attributes. In this study, karyotype analysis and phenotypic morphological and physiological characteristics were compared to explore the differences between the two plant types.

RESULTS

The karyotype analysis of the two cultivars showed that their chromosome types were both tetraploid plants. The results showed that the lignin content in the leaves of 'Red Lion' was high, the cross-sectional structure of the leaf vascular bundle was more stable, and the chlorophyll content was high. In addition, significantly less energy was transferred to the electron transport chain (ETR) during the photoreaction. Similarly, the results regarding the maximum photosynthetic rate (Fv/Fm), nonphotochemical quenching (NPQ) and effective quantum yield of photosystem II photochemistry (△F/Fm') all indicated that the photosynthetic capacity of "Red Lion" was greater than that of "Apple Blossom", which was affected by leaf lodging. The size of the leaves was significantly smaller, and the leaf sag angle, leaf width, and leaf tip angle presented significantly lower values in 'Red Lion' than in 'Apple Blossom', which exhibits leaf sag. The difference in these factors may be the reason for the different phenotypes of the two cultivars.

CONCLUSION

The results of this study proved that lodging affects the photosynthetic capacity of Hippeastrum rutilum and revealed some indexes that might be related to leaf lodging, laying a theoretical foundation for cultivating and improving new varieties.

CRISPR/Cas9-Based RGEN-ISL Allows the Simultaneous and Specific Visualization of Proteins, DNA Repeats, and Sites of DNA Replication

Visualizing the spatiotemporal organization of the genome will improve our understanding of how chromatin structure and function are intertwined. Here, we describe a further development of the CRISPR/Cas9-based RNA-guided endonuclease-in situ labeling (RGEN-ISL) method. RGEN-ISL allowed the differentiation between vertebrate-type (TTAGGG)n and Arabidopsis-type (TTTAGGG)n telomere repeats. Using maize as an example, we established a combination of RGEN-ISL, immunostaining, and EdU labeling to visualize in situ specific repeats, histone marks, and DNA replication sites, respectively. The effects of the non-denaturing RGEN-ISL and standard denaturing FISH on the chromatin structure were compared using super-resolution microscopy. 3D structured illumination microscopy revealed that denaturation and acetic acid fixation impaired and flattened the chromatin. The broad range of adaptability of RGEN-ISL to different combinations of methods has the potential to advance the field of chromosome biology.

Y2SK2 and SK3 type dehydrins from Agapanthus praecox can improve plant stress tolerance and act as multifunctional protectants

Two dehydrins from Agapanthus praecox (ApY₂SK₂ and ApSK₃) show important protective effects under complex stresses. Both ApY₂SK₂ and ApSK₃ contain one intron and consist of a full-length cDNA of 981 bp and 1057 bp encoding 186 and 215 amino acids, respectively. ApY₂SK₂ and ApSK₃ transgenic Arabidopsis thaliana show reduced plasma membrane damage and ROS levels and higher antioxidant activity and photosynthesis capability under salt, osmotic, cold and drought stresses compared with the wild-type. ApY₂SK₂ and ApSK₃ are mainly located in the cytoplasm and cell membrane, and ApY₂SK₂ can even localize in the nucleus. In vitro tests indicate that ApY₂SK₂ and ApSK₃ can effectively protect enzyme activity during the freeze-thaw process, and ApY₂SK₂ also exhibits this function during desiccation treatment. Furthermore, ApY₂SK₂ and ApSK₃ can significantly inhibit hydroxyl radical generation. These two dehydrins can bind metal ions with a binding affinity of Co²⁺> Ni²⁺> Cu²⁺> Fe³⁺; the binding affinity of ApSK₃ is higher than that of ApY₂SK₂. Thus, ApY₂SK₂ has a better protective effect on enzyme activity, and ApSK₃ has stronger metal ion binding function and effect on ROS metabolism. Moreover, plant cryopreservation evaluation tests indicate that ApY₂SK₂ and ApSK₃ transformation can enhance the seedling survival ratio from 23% to 47% and 55%, respectively; the addition of recombinant ApY₂SK₂ and ApSK₃ to plant vitrification solution may increase the survival ratio of wild-type A. thaliana seedlings from 24% to 50% and 46%, respectively. These findings suggest that ApY₂SK₂ and ApSK₃ can effectively improve cell stress tolerance and have great potential for in vivo or in vitro applications.

Amaryllidaceae alkaloids: identification and partial characterization of montanine production in Rhodophiala bifida plant

Rhodophiala bifida (R. bifida) is a representative of the Amaryllidaceae plant family and is rich in montanine, an alkaloid with high pharmaceutical potential. Despite the interest in these compounds, many steps of the biosynthetic pathway have not been elucidated. In this study, we identified the alkaloids produced in different organs of R. bifida under different growth conditions, set up the conditions for in vitro R. bifida regeneration and initiated the molecular characterization of two R. bifida genes involved in alkaloids biosynthesis: the Norbelladine 4'-O-Methyltransferase (RbN4OMT) and the Cytochrome P450 (RbCYP96T). We show that montanine is the main alkaloid produced in the different R. bifida organs and developed a direct organogenesis regeneration protocol, using twin-scale explants cultivated on media enriched with naphthalene acetic acid and benzyladenine. Finally, we analyzed the RbN4OMT and RbCYP96T gene expressions in different organs and culture conditions and compared them to alkaloid production. In different organs of R. bifida young, adult and regenerated plants, as well as under various growing conditions, the transcripts accumulation was correlated with the production of alkaloids. This work provides new tools to improve the production of this important pharmaceutical compound and for future biotechnological studies.

Cloning and characterization of norbelladine synthase catalyzing the first committed reaction in Amaryllidaceae alkaloid biosynthesis

BACKGROUND

Amaryllidaceae alkaloids (AAs) are a large group of plant-specialized metabolites displaying an array of biological and pharmacological properties. Previous investigations on AA biosynthesis have revealed that all AAs share a common precursor, norbelladine, presumably synthesized by an enzyme catalyzing a Mannich reaction involving the condensation of tyramine and 3,4-dihydroxybenzaldehyde. Similar reactions have been reported. Specifically, norcoclaurine synthase (NCS) which catalyzes the condensation of dopamine and 4-hydroxyphenylacetaldehyde as the first step in benzylisoquinoline alkaloid biosynthesis.

RESULTS

With the availability of wild daffodil (Narcissus pseudonarcissus) database, a transcriptome-mining search was performed for NCS orthologs. A candidate gene sequence was identified and named norbelladine synthase (NBS). NpNBS encodes for a small protein of 19 kDa with an anticipated pI of 5.5. Phylogenetic analysis showed that NpNBS belongs to a unique clade of PR10/Bet v1 proteins and shared 41% amino acid identity to opium poppy NCS1. Expression of NpNBS cDNA in Escherichia coli produced a recombinant enzyme able to condense tyramine and 3,4-DHBA into norbelladine as determined by high-resolution tandem mass spectrometry.

CONCLUSIONS

Here, we describe a novel enzyme catalyzing the first committed step of AA biosynthesis, which will facilitate the establishment of metabolic engineering and synthetic biology platforms for the production of AAs.

Cloning and characterization of ApCystatin, a plant cystatin gene from Agapanthus praecox ssp. orientalis responds to abiotic stress

Plant cystatins are involved in the regulation of protein turnover and play important roles in defense mechanisms. We cloned the ApCystatin gene from Agapanthus praecox ssp. orientalis, a famous ornamental and medical plant. The complete cDNA sequence of ApCystatin is comprised of 1439 nucleotides with a 423 bp ORF encoding 140 amino acids. The mRNA level of ApCystatin was significantly up-regulated under various abiotic stress, such as salt, osmosis, oxidative and cold stresses, which suggested that ApCystatin participated in the plant's resistance to stress. The recombinant ApCystatin fusion protein expressed in E. coli transetta (DE3) cells was approximate 18 kDa. 25 μg of ApCystatin inhibited more than 95% activity of papain, suggesting ApCystatin as a papain-like protease inhibitor. As an exogenous substance, 1.60 μg/mL ApCystatin protein improved the regrowth percentage of Arabidopsis 60-h seedlings after cryopreservation from 30% to 47%. In addition, the relative survival rate of A. praecox embryogenic callus after cryopreservation also increased for 30% with addition of 1.20 μg/mL ApCystatin protein. This indicated that ApCystatin performed protective property against cryoinjury to Arabidopsis 60-h seedlings and A. praecox embryogenic callus during cryopreservation. Under various abiotic stress conditions, the recombinant ApCystatin protein showed significant advantage in growth rates at NaCl, mannitol, PEG6000, cold, acidic and alkaline conditions, compared to control. In conclusion, ApCystatin as a new member of plant cystatins exhibited protective property against cryoinjury in plant cryopreservation and abiotic stress in E. coli.

A novel indicator of karyotype evolution in the tribe Leucocoryneae (Allioideae, Amaryllidaceae)

The tribe Leucocoryneae is taxonomically and cytogenetically complex, mainly due to its extraordinary morphological and karyological variation. Robertsonian translocations had long been recognized as a central factor contributing to karyotype diversity within the Leucocoryneae, but so far no major tendency prevailing on the observed complexity of karyotype formula among species has been identified. The assessment of nuclear DNA contents by flow cytometry using propidium iodide in 23 species, representing all genera within the tribe, showed a monoploid genome size variation of 1Cx = 9.07-30.46 pg denoting a threefolds fluctuation. A highly significant linear association between the average DNA content per chromosome arm (2C/FN) and the monoploid genome size (1Cx) is reported for the first time and identified as a novel indicator of a trend governing karyotype diversity within Leucocoryneae. This trend shows that a reduction in DNA content per chromosome arm is influencing and has shaped karyotype evolution of different monophyletic groups within the tribe despite the complex karyotype diversity and apparently contrasting patterns of genome sizes.

O-acetylserine(thio)lyase (OAS-TL) molecular expression in Pancratium maritimum L. (Amaryllidaceae) under salt stress

Different levels of salt stress affected the OAS-TL expression levels in Pancratium maritimum organs (bulb, leaf and root). A detailed method has been described for the identification of the conserved domain of the OAS-TL cDNA in sea daffodil given the scarce data available for the Amaryllidaceae family. Pancratium maritimum or sea daffodil (Amaryllidaceae) is a bulbous geophyte growing on coastal sands. In this study, we investigated the involvement of cysteine synthesis for salt tolerance through the expression of the enzyme O-acetylserine(thio)lyase (OAS-TL) during the stress response to NaCl treatments in P. maritimum. Quantitative real-time PCR was used in different organs (bulb, leaf and root).

The Hippeastrum hybridum PepR1 gene (HpPepR1) encodes a functional guanylyl cyclase and is involved in early response to fungal infection

It is generally known that cyclic GMP widespread in prokaryotic and eukaryotic cells, is involved in essential cellular processes and stress signal transduction. However, in contrast to animals the knowledge about plant guanylyl cyclases (GCs) which catalyze the formation of cGMP from GTP is still quite obscure. Recent studies of plant GCs are focused on identification and functional analysis of a new family of membrane proteins called "moonlighting kinases with GC activity" with guanylyl cyclase catalytic center encapsulated within intracellular kinase domain. Here we report identification and characterization of plasma membrane receptor of peptide signaling molecules - HpPepR1 in Hippeastrum hybridum. Both bioinformatic analysis of amimo acid sequence and in vitro studies revealed that the protein can act as guanylyl cyclase. The predicted amino acid sequence contains highly conserved 14 aa-long search motif in the catalytic center of GCs from lower and higher eukaryotes. Here, we provide experimental evidence to show that the intracellular domain of HpPepR1 can generate cGMP in vitro. Moreover, it was shown that the accumulation of HpPepR1 transcript was sharply increased after Peyronellaea curtisii (=Phoma narcissi) fungal infection, whereas mechanical wounding has no influence on expression profile of studied gene. These results may indicate the participation of cGMP-dependent pathway in rapid, alarm plant reactions induced by pathogen infection.

Transcriptional response of a novel HpCDPK1 kinase gene from Hippeastrum x hybr. to wounding and fungal infection

Calcium dependent protein kinases (CDPK) are well established plant sensor and effectors for calcium ions and participate in regulation of multiple abiotic and biotic stress responses in plant cells. Here we present the identification and characterization of a new CDPK kinase gene from bulbous plant Hippeastrum x hybr. and examine the role of this kinase in stress responses leading to phytoalexin (PA) production in plant tissues. In the previous research, it was shown that Hippeastrum bulbs mechanically wounded or infected with Peyronellaea curtisii (=Phoma narcissi) are inducted to an antifungal red substance synthesis. In this research, we demonstrated Ca²⁺ dependence of the phytoalexin production by wounded bulbs. Furthermore, the isolated HpCDPK1 cDNA for ORF was found to be 1596bp long and encoded 531 amino acid protein with CDPK kinase activity, as was shown by recombinant GST-HpCDPK1 enzyme production and analysis. HpCDPK1 transcript was present in all vegetative and chosen generative organs of Hippeastrum plant. The dynamics of the observed HpCDPK1 mRNA changes in bulbs depended on stressor type. The mechanical injury caused one wave of transcript increase while more complex transcript changes were observed within 48h after Peyronellaea inoculation. In plant bulbs already accumulating red phytoalexin, increases in HpCDPK1 mRNA level were observed at certain intervals within 48h whereas, in the case of fungal infection, only one big increment in the transcript amount at the 10th minute after inoculation was detected. The observed transcriptional response of HpCDPK1 gene to wounding and pathogen infection stress suggests a positive correlation with phytoalexin synthesis and maintenance in bulb tissues and puts more light on CDPK kinase role in the plant stress response regulation. This also bears some potential for understanding the mechanism of a phytoalexin formation.

A Multi-Faceted Approach to Analyse the Effects of Environmental Variables on Geographic Range and Genetic Structure of a Perennial Psammophilous Geophyte: The Case of the Sea Daffodil Pancratium maritimum L. in the Mediterranean Basin

The Mediterranean coastline is a dynamic and complex system which owes its complexity to its past and present vicissitudes, e.g. complex tectonic history, climatic fluctuations, and prolonged coexistence with human activities. A plant species that is widespread in this habitat is the sea daffodil, Pancratium maritimum (Amaryllidaceae), which is a perennial clonal geophyte of the coastal sands of the Mediterranean and neighbouring areas, well adapted to the stressful conditions of sand dune environments. In this study, an integrated approach was used, combining genetic and environmental data with a niche modelling approach, aimed to investigate: (1) the effect of climate change on the geographic range of this species at different times {past (last inter-glacial, LIG; and last glacial maximum, LGM), present (CURR), near-future (FUT)} and (2) the possible influence of environmental variables on the genetic structure of this species in the current period. The genetic results show that 48 sea daffodil populations (867 specimens) display a good genetic diversity in which the marginal populations (i.e. Atlantic Sea populations) present lower values. Recent genetic signature of bottleneck was detected in few populations (8%). The molecular variation was higher within the populations (77%) and two genetic pools were well represented. Comparing the different climatic simulations in time, the global range of this plant increased, and a further extension is foreseen in the near future thanks to projections on the climate of areas currently—more temperate, where our model suggested a forecast for a climate more similar to the Mediterranean coast. A significant positive correlation was observed between the genetic distance and Precipitation of Coldest Quarter variable in current periods. Our analyses support the hypothesis that geomorphology of the Mediterranean coasts, sea currents, and climate have played significant roles in shaping the current genetic structure of the sea daffodil especially during LGM because of strong variation in coastline caused by glaciations.

Leaf patterning of Clivia miniata var. variegata is associated with differential DNA methylation

Leaf patterns (yellow, green and striped) of Clivia miniata var. variegata might be caused by differential DNA methylation in CCGG sites in response to heterogeneous environmental pressure. Clivia miniata is an important ornamental plant.Clivia miniata var. variegata (Cmvv) is a variegated leaf mutant of C. miniata. Typical Cmvv has attractive green and yellow-stripped leaves. The study has revealed that an explant of Cmvv, even a full-green explant, could regenerate plants of three different types: yellow, green, ands triped; normal-appearing chloroplasts were found in guard cells but not in mesophyll cells of all the three types of Cmvv using confocal laser scanning microscopy (CLSM).Thus, we speculated that cells of the three types of Cmvv had an identical mutation and the mutation might disturb mesophyll cell chloroplast biogenesis after symplastic isolation of guard cells. Using CLSM and methylation sensitive amplification polymorphism (MSAP), we found that (a) striped leaves of Cmvv are due to sectorial decreases in chlorophyll levels and the decreases are associated with CG hypermethylation; (b) extent of epigenetic divergence among the three types of Cmvv leaves is positively correlated with intensity of leaf-color difference; and (c) green stripes of two plants are clustered in one group based on the MSAP profiles, but green and yellow stripes of a plant are not. Sequencing analysis indicated that CG hypermethylation in gene bodies of CPSAR1 and ycf2 might lead to gene silencing and yellow leaves/stripes of Cmvv. All together, it is possible that cytosine methylation involved regulating leaf color of Cmvv, also striped pattern of Cmvv might be caused by differential DNA methylation in response to heterogeneous environmental pressure. Furthermore, a novel leaf-color epigenetic hypothesis was proposed in this article.

Identification of a Hippeastrum hybridum guanylyl cyclase responsive to wounding and pathogen infection

Guanosine 3',5'-cyclic monophosphate (cGMP) is a critical component of many (patho)physiological processes in plants whilst guanylyl cyclases (GCs) which catalyse the formation of cGMP from GTP have remained somewhat elusive. Consequently, the two major aims are the discovery of novel guanylyl cyclases and the identification of GC/cGMP mediated processes. To identify a novel GC from Hippeastrum hybridum plant and facilitate the preparation of guanylyl cyclase in an amount sufficient for further crystallographic studies, we have constructed an overproduction system for this enzyme. This gene encodes a protein of 256 amino acids, with a calculated molecular mass of 28kD. The predicted amino acid sequence contains all the typical features and shows a high identity to other plant GCs. The GST-HpGC1 was catalytically active in Escherichia coli cells and the purified, recombinant HpGC1 was able to convert GTP to cGMP in the presence of divalent cations. The used overexpression system yields a guanylyl cyclase as 6% of the bacterial cytosolic protein. Besides the identification of HpGC1 as a guanylyl cyclase, the study has shown that the level of HpCG1 mRNA changed during stress conditions. Both mechanical damage and a Peyronellaea curtisii (=Phoma narcissi) fungi infection led to an initial decrease in the HpGC1 transcript level, followed by a substantial increase during the remainder of the 48-h test cycle. Moreover, significant changes in cyclic GMP level were observed, taking the form of oscillations. In conclusion, our data unequivocally identified the product of the HpGC1 gene as a guanylyl cyclase and demonstrates that such an overproduction system can be successfully used in enzyme synthesis. Furthermore, they indicate a link between the causing stimulus (wounding, infection) and guanylyl cyclase expression and the increase in cGMP amplitude. Therefore, it is concluded that appearance of cyclic GMP as a mediator in defense and wound-healing mechanisms provides a clue to the regulation of these processes.